# Missing symbols in the sansmath package

When using the sansmath package with the Arev font, symbols like + and = fail to appear in the compiled document.

\documentclass{article}
\usepackage{fouriernc} % use the Arev font
\usepackage{sansmath}
\begin{document}
You can see this $+$ and this $=$.
But you can't see \sansmath this $+$ and this $=$.
\end{document}


If, however, I switch the order of \usepackage to include sansmath first and then fouriernc, for some reason you now can see the symbols, but I get two errors...

\documentclass{article}
\usepackage{sansmath}
\usepackage{fouriernc} % use the Arev font
\begin{document}
You can see this $+$ and this $=$.
Now you can see \sansmath this $+$ and this $=$, but there are 2 errors.
\end{document}


! LaTeX Error: Command \mathrm' already defined.

! LaTeX Error: Command \mathrm' already defined.

-

The package fouriernc doesn't use Arev fonts, but rather NewCentury Schoolbook and a modified version of the Fourier math fonts.

These fonts have different symbol positions and so they define + and = differently from normal: the normal mathcode of + is "202B (in hexadecimal form), while fouriernc uses "2280.

These cryptic codes say: + is an operation symbol (first digit 2), which comes from math family 0 (in the standard setting) or 2 (in the fouriernc settings). The symbol lives in font position "2B (standard setting) or "80 (fouriernc).

The package sansmath expects standard codes; in family 2 it uses cmsy10 which in position "80 has nothing (it's a seven bit font).

So the two packages are completely incompatible.

-
Thanks, but then do you have an alternative to the answer to my question here? tex.stackexchange.com/a/44926/9757 (the comments are relevant). Is there another font/package that will change my Fourier math fonts? –  jamaicanworm Feb 20 '12 at 23:14
The alternatives are: not using math in captions or not using a sans serif font in captions. Sorry: reverting all the math codes when switching to \sansmath is a job that nobody would undertake. –  egreg Feb 20 '12 at 23:22
I'm fine with not using a sans serif font; the original question was to just have the font in my overpic captions be different from my main font (including in math mode). Is there another (non-sans-serif) solution for this? –  jamaicanworm Feb 20 '12 at 23:24
Two different serif fonts are quite difficult to combine, but even if they existed, the problem would be just the same: if the main font changes the math codes, also the other font should use the same conventions (or the big work of doing a reversal each time one switches font family should be carried out). –  egreg Feb 20 '12 at 23:33
It's theoretically possible: take the huge default math symbol table and keep it somewhere to be called when you want \sansmath. Practical? No, sorry. This table is built in a large number of steps and keeping track of it is a herculean task. –  egreg Feb 21 '12 at 0:41